The mechanism(s) underlying how mutations in emerin, an inner nuclear envelope protein, cause muscle disease remain unknown. Mutations in the gene encoding emerin cause Emery-Dreifuss Muscular Dystrophy (EDMD), characterized by progressive skeletal muscle wasting, irregular heart rhythms and tendon contractures. The skeletal muscle phenotype is caused by the failure to regenerate skeletal muscle. Skeletal muscle stem cell differentiation requires the coordinated temporal expression of differentiation genes. Disruption of the differentiation transcriptional program causes impaired differentiation. Genomic architecture controls gene activation or repression by regulating the association of the genome with transcriptionally active or repressed nuclear domains. The genome reorganizes itself during differentiation of many cell types to control coordinated temporal gene expression. This reorganization plays fundamental roles in cell fate decisions during stem cell differentiation and in development. The research proposed here will examine how emerin regulates genomic organization and gene expression to regulate the coordinated temporal gene expression required for myogenic differentiation and how this is altered in EDMD. The field lacks a fundamental understanding of the mechanisms regulating nuclear lamina regulation of genomic architecture and its affect on gene expression. The nuclear lamina regulates genomic organization and chromatin architecture. However, the lamins are not required for repressed chromatin localization at the nuclear periphery, suggesting other nuclear envelope proteins mediate their association. We hypothesize emerin is one of these proteins that mediates the association of repressed chromatin with the nuclear envelope. Supporting our hypothesis emerin interacts with repressive chromatin machinery and dynamically interacts with myogenic differentiation gene loci during differentiation; this localization is emerin-dependent. The proposed studies will test how the interaction of emerin with histone deacetylase 3 (HDAC3) establishes or maintains repressive chromatin at the nuclear envelope. Emerin regulation of HDAC3 activity is predicted to regulate genomic reorganization and coordinated temporal expression of differentiation genes during differentiation. Thus we will monitor gene expression during emerin-null myogenic progenitor differentiation to identify molecular pathways disrupted in these cells, which will be confirmed by treatment with activators or inhibitors. EDMD-causing emerin mutant progenitors will be used to confirm these pathways are involved in the impaired differentiation seen in EDMD. These studies will have a significant impact on muscle disease because they analyze specific molecular interactions mediating genomic organization at the nuclear envelope and how their disruption alters transcriptional programing during differentiation and in muscle disease.